Microamperage electrical stimulation ( MENS) is a modality widely used by physical therapists for pain relief and tissue repair. Manufacturers of MENS units have claimed that increased ATP levels result from these stimulation units, though the mechanism of action is unknown and may be dependent on various stimulation paradigms. Studies have been done which establish the link between MENS and ATP synthesis in rat skin (Cheng, et. al., 1982). However, there is a dearth of information on the effect of MENS on ATP in human tissue, despite the FDA approval of MENS units and the wide use of these units in rehabilitative therapy. The purpose of this study is to examine the effect of MENS on muscle metabolism in the human masseter using Magnetic Resonance Spectroscopy (MRS). MRS can objectively evaluate the efficacy of MENS using phosphorous metabolite spectra to measure Pi, Phosphocreatine, and ATP peak areas and ratios. Temporomandibular joint disorder/dysfunction (TMJ) patients will be used in this study to help determine if the MENS units increase the rate of ATP production (which would be expected to aid in tissue repair and pain relief) in damaged or weak tissue. We hypothesize that MENS stimulation will change muscle pH and consumption of phosphorous containing compounds in the TMJ cohort but will not affect the normal population. The pilot study includes both normal and TMJ patients with varying parameters of stimulation to detect optimal levels of stimulation. Once completed, a double blind study will proceed using MRS on normal and TMJ patients with consistent stimulation parameters to measure muscle metabolite levels prior to and during exposure to MENS. Coils will be placed on both masseter muscles in order to measure changes in the metabolite levels in each muscle. Pilot data on 18 normal subjects has not shown ATP level changes with various stimulation parameters, which is in keeping with our hypothesis.